CD28 Signals in the Immature Immunological Synapse

Abstract

T cell recognition of peptide-MHC complexes on APCs results in the aggregation of TCRs at a central supramolecular activation complex (c-SMAC) within a mature immunological synapse. T cells require a second “costimulatory” signal for activation, the most important of which, for naive T cells, is from CD28. However the time at which CD28-derived signals are induced relative to c-SMAC formation is not well understood. In this study, we have assessed the kinetics of CD28 localization and function relative to well-established aspects of c-SMAC formation. CD28 accumulates at the immature synapse alongside the TCR and is likewise enriched at the synapse at the onset of the calcium signal. In addition, using CD28 deficient or reconstituted murine cells in a single-cell recording approach shows that CD28 regulates this signal within seconds of a TCR-mediated rise in intracellular calcium levels. Finally, CD28 exerts effects on both the initiation and stabilization of the synapse in parallel with its effects on the downstream proliferation of T cells. Together, the data show that CD28 functions in the immunological synapse before the formation of the c-SMAC.

T-cell triggering thresholds are modulated by the number of antigen within individual T-cell receptor clusters

“…Additionally, the apparent magnitude of Ca 2þ flux was increased, in a manner similar to that observed with the coagonist ER60 peptide. This stronger activation with CD80-CD28 costimulation has been observed before (29).…”

“…However, ER60 did yield an apparent increase in the magnitude of Ca 2þ flux. The costimulatory molecule CD80 can also modulate T-cell signaling by activating CD28 on the T-cell surface (29,30). Inclusion of CD80 (approximately 300 molecules μm −2 ) (14) in the supported membrane during MCC:T102E titration experiments yields two distinct effects on TCR signaling (Fig.…”

CD28 Inhibits T Cell Adhesion by Recruiting CAPRI to the Plasma Membrane

“…Additionally, despite lacking a signaling system that is ostensibly stimulatory, CD28-deficient T cells (CD4 + CD28 2 ) infiltrate peripheral tissues (synovial tissue) in an autoimmune-like response, suggesting that CD28 might have a role in downregulating adhesion and trafficking to inflamed organs (14,15). Our data that CD28 is in some aspects (e.g., adhesion) inhibitory represents a paradigmatic shift and is the first step in gaining a better understanding of specific CD28 pathways necessary to develop therapeutics selectively targeting proinflammatory pathways downstream of CD28.…”

Controlling NF-κB activation in T cells by costimulatory receptors

“…CD28 accumulates in the synapse at very early time points at the onset of the calcium signal. While some reports show a role of CD28 for the formation and stabilization of the mature immunologic synapse and c-SMAC localization of PKCy, 38,39 quantitative imaging failed to substantiate these findings. 40 Life cell imaging approaches showed a surprisingly complex and highly dynamic shuttling of NF-kB activating signalling molecules between the c-SMAC and punctuated structures in the cytosol, 41 but the nature and function of these structures need further investigations.…”